Three primary lines of effort are being pursued. The first is concerned with the identification, separation and purification of various transplantation antigens from human cells with the prime objective of (a) characterizing the various transplantation antigens in human cells, (b) isolating the individual antigens in amounts large enough to permit detailed studies of the chemical structure of the antigenic components and detailed studies of the biological activities in transplantation reactions and (c) the production of typing sera against pure HL-A antigens. The second line of effort is concerned with antibody production by established lines of human cells and with ancillary cellular biological applications of cultured cells. The third is the production of large scale cell cultures of human lymphocytes and the collection of human cell lines for the above studies. We are utilizing the large scale cell culture units to produce cells for these studies on cell membrane antigens and to continue our efforts in studies on experimental approaches to lymphoid cell differentiation and antibody synthesis in vitro. By the isolation of major transplantation antigens from cultured human lymphocytes, and the production of isoantibodies specific to transplantation antigens by cultured human cell lines, we hope to add new dimensions to the control of immunological barriers in organ transplantation. The availability of purified human transplantation antigens would enable the study of low- zone tolerance in the prospective recipient of an organ graft. Likewise, the suppression of reactions to transplantation antigens by anti-lymphocytic antisera produced by cultured human lymphoid cells would be preferable to the present heterologous sources of serum and should obviate the serum sickness reactions during serum administration. Furthermore, the production of antibodies by cultured human cells against various pathogens has the same advantages.